# Physics

A wheel has a coonstant rotational acceleration of 3.0 rad/s^2. During a certain 4.0 s interval, it turns through an angle of 120 rad. Assuming that the wheel starts from rest, how long is it in motion at the start of the 4s interval.

I just need help in getting started. I know that the 3.0 rad/s^2 is the alpha roational acceleration and 120 rad is the theta. I do not have though rotational velocity.

Thank you

The way you ask the question does not make sense. At the START of the 4s interval, it is at rest, and you are asking "how long is it in motion?" At the start of the interval, it has not been in motion at all. You have already told us how long it is in motion, so why are you asking "how long"?

Perhaps you meant to ask how large an angle it turns through AT THE END OF 4 seconds. In that case,

Total angle of rotation = (1/2)*alpha* t^2

The displacement from t=0 is not 120, but 120 plus the displacement starting at the four second period

totaldisplacement=initialdisplacement + initalangularspeed*time + 1/2 angular acceleration*time^2
Starting from rest...

120+ initialdisplacement= +0+ 1/2*3 (t )^2

solve for t. this is the time from starting to the end of the four second period.

Now, initial displacement is 1/2*3(t-4)^2
so
120+1/2*3(t-4)^2=1/2*3 (t )^2
solve for t. You are looking for t-4 in this problem.

check my thinking.

1. 👍 0
2. 👎 0
3. 👁 143
asked by laura

## Similar Questions

1. ### physics

A wheel has a rotational velocity of 18·rad/s counterclockwise. You place you hand against the wheel and the friction between your hand and the rim stops it. (a) If it takes 4·s to stop the wheel, what is its rotational

asked by jack on February 6, 2015
2. ### physics

Starting from rest at t = 0 s, a wheel undergoes a constant angular acceleration. When t = 1.6 s, the angular velocity of the wheel is 5.5 rad/s. The acceleration continues until t = 17 s, when the acceleration abruptly changes to

asked by Katie on March 5, 2012
3. ### physics

Starting from rest at t = 0 s, a wheel undergoes a constant angular acceleration. When t = 1.6 s, the angular velocity of the wheel is 5.5 rad/s. The acceleration continues until t = 17 s, when the acceleration abruptly changes to

asked by Katie on March 11, 2012
4. ### Physics

Starting from rest at t = 0 s, a wheel undergoes a constant angular acceleration. When t = 1.6 s, the angular velocity of the wheel is 5.9 rad/s. The acceleration continues until t = 19 s, when the acceleration abruptly changes to

asked by Julia on November 4, 2015
5. ### Physics

A spinning wheel is slowed down by a brake, giving it a constant angular acceleration of −4.60 rad/s2. During a 2.60-s time interval, the wheel rotates through 85.4 rad. What is the angular speed of the wheel at the end of the

asked by Mack on April 8, 2015
6. ### physics

A wheel, starting from rest, has a constant angular acceleration of 1.3 rad/s2. In a 2.5-s interval, it turns through an angle of 98 rad. How long has the wheel been in motion at the start of this 2.5-s interval?

asked by shelby on March 17, 2008
7. ### Physics 111-1

A wheel, starting from rest, has a constant angular acceleration of 1.8 rad/s2. In a 3.7-s interval, it turns through an angle of 52 rad. How long has the wheel been in motion at the start of this 3.7-s interval?

asked by Paula on November 18, 2012
8. ### physics

A wheel, starting from rest, has a constant angular acceleration of 1.8 rad/s^2. In a 3.1-s interval, it turns through an angle of 142 rad. How long has the wheel been in motion at the start of this 3.1-s interval?

asked by Tsion on April 2, 2014
9. ### physics

A 4.50-kg wheel that is 34.5 cm in diameter rotates through an angle of 13.8 rad as it slows down uniformly from 22.0 rad/s to 13.5 rad/s. What is the magnitude of the angular acceleration of the wheel? A) 0.616 rad/s 2 B) 22.5

asked by help me!!! on June 28, 2012
10. ### physics

An electric motor rotating a workshop grinding wheel at a rate of 9.80 101 rev/min is switched off. Assume the wheel has a constant negative angular acceleration of magnitude 2.00 rad/s2. (a) How long does it take for the grinding

asked by monic on November 14, 2012

More Similar Questions